1. Field of Invention
This invention relates to an illuminator apparatus usable with a scanner device, such as a document scanner or a facsimile machine. More particularly, this invention is directed to a multi-colored illuminator apparatus usable with a scanner device capable of scanning multi-colored documents.
2. Description of Related Art
Conventional scanners allow a computer to convert text, a drawing or a photograph into digital information so that a graphics or desktop publishing program can use the digital information to display the image of the text, drawing or photograph onto a display screen or to reproduce the image with a graphics printer. Some conventional scanners distinguish between only black and white colors which can be useful for text or line art. More sophisticated scanners can differentiate between shades of gray. Even more sophisticated scanners can differentiate among colors and use red, blue and green filters to detect the colors in the reflected light.
Many conventional scanners use either fluorescent or incandescent illuminators to illuminate the text, drawing or photograph during scanning. Fluorescent or incandescent illumination is adequate for black and white scanners, as well as for those scanners that can differentiate shades of gray. Black-and-white and gray-shading scanning requires only one pass of a scan head in a slow scanning direction adjacent the scanned document. For a conventional multi-pass color scanner, the document is scanned multiple times, and each time the illumination on the document is filtered to pass a different color region of the light onto the document and, in turn, onto the image sensing detectors. For a conventional single-pass color scanner, the red, green and blue image sensing pixels in the image sensing detector use red, green and blue color filters. In conventional multi-pass and single-pass scanners, the filters discard on average more than two-thirds of the light reaching the pixel, lowering the overall illumination efficiency of the system.
Instead of fluorescent or incandescent illuminators, one manufacturer uses an illuminator that includes a single row of red, green and blue diodes as the light source. As stated above, scanning is achieved using a multi-pass scanner or a single-pass scanner.
Regardless of the type of illuminator used in the conventional scanner devices, the document is illuminated with white light, i.e., the various spectral regions corresponding to red, green and blue which are intermixed at the source of the illumination. The light is reflected off the document and imaged onto light-sensitive detectors. These detectors are often referred to as photodiode arrays or "charge coupled devices" or "CCDs". Using only a single line of white light across the document being scanned results in a rather inefficient use of the color components of the light.